题解 | #单链表的排序#

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */
//归并排序
public class Solution {
    /**
     * 
     * @param head ListNode类 the head node
     * @return ListNode类
     */
    public ListNode sortInList (ListNode head) {
        // write code here、
        if(head == null || head.next == null){
              return head;
        }
        ListNode fast = head.next;
        ListNode slow = head;
        while(fast != null && fast.next != null){
            fast = fast.next.next;
            slow = slow.next;
        }
        ListNode flu = slow.next;
        slow.next = null;
        ListNode left = sortInList(head);
        ListNode right = sortInList(flu);
        ListNode node = new ListNode(-1);
        ListNode pre = node;
        while(left != null && right != null){
            if(left.val < right.val){
                pre.next = left;
                left  = left.next;
            }else{
                pre.next = right;
                right  = right.next;
            }
            pre =  pre.next;
        }
        if(left != null){
             pre.next = left;
        }else{
             pre.next = right;
        }
        return node.next;
    }
}